1. Field of the Invention
This invention relates to method and apparatus for generating electrically charged or uncharged particles in an electron cyclotron resonator by generating a magnetic field for resonance tuning of the electron cyclotron resonator.
2. Description of the Prior Art
In the microstructure technique, for instance in the manufacture of semiconductor structural elements or in the coating of materials with thin films, charged and uncharged particles are necessary which are used for etching or coating. For the production of these charged and uncharged particles controllable plasma or ion sources which make available a maximum density of the particles required in each instance. For example, for many application cases it is desirable that ion densities of more than 10.sup.11 cm.sup.-3 are permitted with acceptable density distribution within the plasma which for example corresponds to an argon ion saturation current density of more than 10 mA/cm.sup.2.
In order to be able to fulfil these high requirements numerous plasma and ion sources have already been suggested which rest on the most diverse principles. With the more recent plasma and ion sources in particular the principle of the electron cyclotron resonance (=ECR) in the technical microwave frequency of 2.45 GHz is applied.
For example plasma processors are known which have a high-frequency waveguide in which a glass tube is disposed for the reception of the plasma wherein by means of current-carrying coils a magnetic field is generated permeating the plasma (DE-OS No. 37 29 347). Of disadvantage in such plasma processors is that substrates with large diameter cannot be worked uniformly with a plasma. In addition, the air-cored coil which must often be encapsulated water-tight and in a special steel has a very high power requirement.
Furthermore a multipolar microwave arrangement for the generation of plasma for etching and deposition is known in which the magnetic field which fulfills the ECR condition is present in the process chamber at a distance of only a few millimeters from each pole surface (R. Burke, C. Pomot: Microwave Multipolar Plasma for Etching and Deposition; Solid State Technology, February 1988, pages 67 to 71). Several cylindrical conductors of which each is disposed a few millimeters above the pole surface of a magnet function herein as feed of the microwave energy into the plasma. Of disadvantage in this only locally effective permanent magnet arrangement is that the ECR zones are only generated at the periphery of the particular plasma volumes. The ratio "ECR volume" to the total plasma volume with increasingly larger plasma sources is reduced to increasingly smaller values, i.e. this type of ECR excitation becomes more unfavorable with increasing size of the sources.
Lastly, a plasma source is also known which rests on the ECR principle and in which the microwave power is applied in a resonator with the plasma as load (USP 3 778 656). The tuning of this resonator, however, takes place purely mechanically in that for example a screw is turned into or out of the resonator.